Manufacture of dome-shaped articles from thermoplastic foam sheet material technical field

ABSTRACT

Apparatus for making a dome-shaped sealing element for a vaginal speculum from an annular workpiece ( 37 ) of closed cell polyethylene foam sheet material comprising a mould ( 28 ) defining an open ended cavity having a circular cross-sectional shape smaller in diameter than the outside diameter of the workpiece, a loading station ( 32 ) wherein said workpiece may be applied to the mould to rest on the mould to cover a mouth of said cavity, an insertion station ( 33 ) wherein a plunger with a convex head forces the workpiece into said cavity so as to cause the workpiece to adopt a domed shape with a concave side directed towards the mouth of the cavity, a heating station ( 34 ) wherein radiant heating means heat the concave side of the workpiece in the mould cavity to soften a surface layer thereof, a cooling station ( 35 ) wherein the said surface layer is allowed to cool in the mould cavity, and an unloading station ( 36 ) wherein a plunger with a concave head pushes the shaped workpiece from the cavity, conveyor means to shift the mould from station to station, and control means to effect coordinated operation of the conveyor means and the respective plungers and radiant heating means.

TECHNICAL FIELD

[0001] This invention relates to the formation of dome-shaped articles,for example segments of a hollow sphere, ellipsoid, paraboloid or othersmoothly curved solid of revolution, from initially substantially planarworkpieces of thermoplastic foam sheet material.

[0002] One such article is useable as a sealing element, for a tubularvaginal speculum, of the kind that effects a seal between the speculumand the tissue defining the vaginal passage near the vaginal orifice.The present invention was devised with that application in mind and isdescribed hereinafter primarily with reference thereto.

BACKGROUND ART

[0003] Insofar as a vaginal speculum sealing element is concerned, theonly relevant background art known to the applicant is the speculum andsealing element described and claimed in applicants' earlierInternational patent application No. PCT/AU00/00267.

[0004] Insofar as the manufacture of shaped thermoplastic foam articlesin general is concerned, typical prior art processes include injectionmoulding of mixtures of polymer and expansion agents, extrusion of suchmixtures, cutting or sculpting stock slabs or sheets of foam with sharpknives or heated elements, and roll-forming or press-forming previouslywarmed foam sheet or strip.

SUMMARY OF THE INVENTION

[0005] Internal vaginal sealing elements must meet certain criteria notnecessarily applicable to thermoplastic foam articles generally. Theymust be sterile and thus manufactured by a machine operable by a personusing gloves, so as to come to the patient untouched by human hand.

[0006] Preferably the sealing element has a smooth resilient outersurface layer to promote sealing and reduce discomfort to the womanbeing examined.

[0007] Still further, as it is public policy for many Governments toencourage mass screening of women by means of a vaginal speculum todetect the onset of cervical cancer at an early stage of itsdevelopment, it is essential that the process of manufacture of thesealing element for such a speculum is both quick and automatic toenable the finished sealing element to be inexpensive and thus adaptedfor use as a single use disposable item.

[0008] An object of the present invention is to provide a method andapparatus for making vaginal speculum sealing elements, which meet allof the above-mentioned criteria.

[0009] In its broadest aspect the invention consists in a method ofmaking a dome-shaped article from a workpiece of thermoplastics sheetmaterial, comprising the steps of selecting a workpiece ofthermoplastics foam sheet material in the form of a substantially flat,flexible disk having a smoothly curved periphery, forcing the workpieceinto a mould cavity having a cross-section with a periphery ofsubstantially the same shape as that of the workpiece but of smallersize, so as to cause the workpiece to adopt a domed shape displaying aconcave side, heating said concave side to soften a surface layerthereof, then ceasing said heating to allow said surface layer to cooland harden to cause the workpiece to become self-sustaining in shape,and then removing the shaped workpiece from the mould cavity.

[0010] In preferred versions of the invention as applied to themanufacture of a sealing element for a vaginal speculum, the workpieceperiphery may be a circle. Furthermore, the workpiece may be pierced bya centrally placed hole, such that the finished sealing element, as itcomes from the mould cavity, has a clearance hole at the apex of thedome through which the speculum may extend with an interference fit. Inthe most preferred embodiments the annular workpiece is dimensioned suchthe dome-shaped sealing element is substantially a hemi-sphere. In lesspreferred embodiments such a hole may be cut in the dome-shaped elementafter its removal from the mould cavity.

[0011] According to a second aspect of the invention it comprisesapparatus for effecting the method of the invention comprising a moulddefining said cavity, a loading station wherein said workpiece may beapplied to the mould to rest on the mould to cover a mouth of saidcavity, an insertion station wherein insertion means force the workpieceinto said cavity so as to cause the workpiece to adopt a domed shapewith a concave side directed towards the mouth of the cavity, a heatingstation wherein heating means heat the concave side of the workpiece inthe mould cavity, a cooling station wherein the heated concave side ofthe workpiece is allowed to cool in the mould cavity, and an unloadingstation wherein ejection means remove the shaped workpiece from thecavity, conveyor means to shift the mould from station to station, andcontrol means to effect coordinated operation of the conveyor means andthe insertion means, heating means and ejection means.

[0012] For preference the mould is one of a batch of moulds shifted asone from station to station and the insertion means, heating means andejection means operate simultaneously on each mould of the batch in theinsertion station, heating station and unloading station respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] By way of example an embodiment of the above-described inventionis described in more detail hereinafter with reference to theaccompanying drawings.

[0014]FIG. 1 is a diagrammatic side elevation of an apparatus accordingto the invention.

[0015]FIG. 2 is a diagrammatic plan view of the apparatus of FIG. 1drawn to a smaller scale.

[0016]FIG. 3 is an isometric view of a mould, being a component of theapparatus of FIG. 1 drawn to an enlarged scale.

[0017]FIG. 4 is a diagrammatic side elevation of a loading station ofthe apparatus of FIG. 1 drawn to a larger scale.

[0018]FIG. 5 is a diagrammatic side elevation of an insertion station ofthe apparatus of FIG. 1 drawn to a larger scale, showing the insertionmeans of that station at the upper end of an operating stroke.

[0019]FIG. 6 is a view similar to FIG. 5 showing the insertion means atthe lower end of an operating stroke.

[0020]FIG. 7 is a diagrammatic side elevation of a heating station ofthe apparatus of FIG. 1 drawn to a larger scale.

[0021]FIG. 8 is a diagrammatic side elevation of an unloading station ofthe apparatus of FIG. 1 drawn to a larger scale, showing the ejectionmeans of that station at the upper end of an operating stroke.

[0022]FIG. 9 is a view similar to FIG. 8 showing the ejection means atthe lower end of an operating stroke.

[0023]FIG. 10 is a sectional elevation of a single mould of a batch ofmoulds in the loading station of FIG. 4 drawn to a larger scale.

[0024]FIG. 11 is a sectional elevation of a single unit of the insertionmeans shown in FIG. 5 drawn to a larger scale.

[0025]FIG. 12 is a sectional elevation of a single unit of the insertionmeans shown in FIG. 6 drawn to a larger scale.

[0026]FIG. 13 is a partly sectioned side elevation of a single unit ofthe heating means shown in FIG. 7 drawn to a larger scale.

[0027]FIG. 14 is a partly sectioned side elevation of a single unit ofthe ejection means shown in FIG. 8 drawn to a larger scale.

[0028]FIG. 15 is a partly sectioned side elevation of a single unit ofthe ejection means shown in FIG. 9 drawn to a larger scale.

BEST MODE OF PUTTING THE INVENTION INTO EFFECT

[0029] The apparatus illustrated by the drawings is suitable for theproduction of vaginal probe sealing elements.

[0030] It comprises a structural frame comprising posts 20, longitudinalrails 21 and transverse rails 22 supporting the operative components ofthe apparatus. Those operative components include conveyor meanscomprising driven sprockets 23, driving sprockets 24 rotated in unisonby a gear motor 25, two conveyor chains 26 trained around respectivepairs of the sprockets and a plurality of channel-sectioned cross-beams27 extending between and secured to corresponding links of the chains26.

[0031] Each cross-beam 27 has a row of open ended, generally cylindricalmoulds 28 secured to the web of the cross-beam 27. As can best be seenin FIG. 10, each mould 28 is secured to its associated cross-beam 27 bytwo flat-head machine screws 29 extending through counter-sunk clearanceholes 30 (see FIG. 3) within the wall thickness of the mould intothreaded bores in bosses 31 fixed to the web of the cross-beam 27.Furthermore each web of the cross-beam is pierced by openings inrespective alignment with the mould cavities so that (as will be madeclear below) a shaped or completed workpiece (although normally retainedin the cavity of a mould by friction) may be readily pushed from themould cavity through the corresponding hole in the cross-beam, as andwhen required.

[0032] The illustrated apparatus operates on successive, spaced apartbatches of workpieces as they progress from station to station throughthe apparatus. To that end the cross-beams 27 are arranged in spacedapart groups. In the present instance there are three cross-beams 27 ineach group and there are nineteen moulds 28 on each beam. Thus, batchesof fifty-seven moulds may be shifted from station to station forsimultaneous operation on that number of workpieces in each station, byappropriate intermittent operation of the conveyor means. The dwell timein all of the stations is thus equal to that of the station requiringthe longest time to process a batch of workpieces. Usually that sloweststation is the loading station.

[0033] There are five such stations, namely a loading station 32, aninsertion station 33, a heating station 34, a cooling station 35 and anunloading station 36.

[0034] The loading station 32 is no more than an exposed portion of theupper flight of the conveyor means at a height above floor level suchthan one or more operators or an automated loading mechanism (notshown), may conveniently load a workpiece 37 onto each mould 28 in theloading station while the conveyor means are stationary.

[0035] In the present instance each workpiece 37 is an annuluspreviously cut from a flat sheet of a relatively dense, closed cell,pharmaceutically acceptable, thermoplastics foam, for examplepolyethylene foam. The foam is resilient and smooth surfaced. The outerdiameter of the annulus is such that the finished dome-shaped workpieceis adapted for use as a sealing element for a vaginal speculum. Thecentral hole 38 (see FIG. 10) of the annular workpiece is sized toaccommodate a tubular probe of a vaginal speculum extending neatlythrough that hole. The fit between the workpiece and probe issufficiently tight to ensure that the junction between the probe and thefinished sealing element is able to withstand the required air pressurewithin the vagina without substantial leakage.

[0036] The workpieces may be pre-cut from a stock sheet of thermoplasticfoam by a conventional, automatic cutting machine. For example, amachine comprising a reciprocating cutting head furnished with circularknives, which cut through the sheet against a cutting table, as thesheet is drawn across the table intermittently, in synchronism with therise and fall of the cutting head. Such machines are well known andrequire no further description herein.

[0037] Each mould 28 (see FIG. 3) has a peripheral locating flange 39adapted to partly surround the annular workpiece when loaded onto themould to ensure that the workpiece is then co-axial with the mould. Inthis embodiment the flange 39 has two gaps in it to provide clearancebetween the flange and the heating means, as the moulds are moved thoughthe heating station.

[0038] Once the moulds have been loaded at the loading station theoperator may press a push button or otherwise send a start signal tocontrol means including a Programmable Logic Array (PLA) or aprogrammable logic controller, or other like “computerised’ controller,providing for automatic operation of the apparatus. If all of thesucceeding stations are in the “ready” condition, that is to say theoperating means in each station have completed their precedingoperation, the control means energise the conveyor means, so as toadvance each batch of moulds from one operating station to the next.Thus the loaded batch of moulds in the loading station 32 is advanced tothe insertion station 33.

[0039] The insertion means at the insertion station (see FIGS. 5 and 6)comprise a platen frame 40 able to rise and fall under the influence oftwo double acting pneumatic thrustors 41 (one near each end of the frame41) on two pairs of guide rods 42, and fifty-seven plungers 43 inrespective alignment with the moulds in the insertion station.

[0040] As may best be seen in FIGS. 11 and 12, each plunger 43 comprisesa plunger rod 44 and a hemi-spherical plunger head 45. The curved convexsurface of the plunger head 45 preferably conforms to the requiredconcave surface of the finished sealing element. As the plunger 43descends from the upper (FIG. 11) position to the lower (FIG. 12)position it pushes the workpiece 37 ahead of it into the mould cavity,causing it to adopt the required domed shape.

[0041] It will be noted that the plunger head 45 is furnished with adownwardly projecting a central boss 46. That boss serves to displaceany wad of the original sheet material that may be retained in thecentral hole of the annular workpiece.

[0042] When the plunger retracts to the upper position the domedworkpiece 37 is retained by friction within the mould cavity, as shownin FIG. 13.

[0043] If and when a further start signal is given to the PLA and all ofthe stations are once more ready, the conveyor means are caused to movethrough a further step and deliver the moulds holding the domedworkpieces from the injection station 33 to the heating station 34.

[0044] As may best be seen from FIG. 7, heating station 34 comprises aplaten frame 47 able to rise and fall on guide rods 48 under the actionof a pneumatic thrustor 49 and supporting an array of fifty-sevenheating units 50. The heating units 50 are in respective alignment withthe moulds 28 as delivered into the heating station.

[0045] As may best be seen from FIG. 13, each heating unit 50 comprisesa generally frusto-conical heat shield 51 disposed above a conventionallow voltage lamp assembly including a miniature luminaire 52. Suchassemblies and their miniature luminaires are well known for use as spotlamps in building illumination systems. The luminaire comprises agenerally parabolic reflector 53 with a colourless transparent window 54closing the otherwise open end of the reflector and a miniatureincandescent light bulb (not shown) mounted within the reflector with anincandescent element substantially coinciding with the focus of thereflector. Although primarily intended for the production of light, suchlight bulbs also generate considerable heat. That heat is radiatedthrough the window 54 onto the concave surface of the correspondingworkpiece 37.

[0046] The radiated heat impinging on the workpiece raises thetemperature of a concave surface layer thereof. The temperature reacheddepends primarily on the wattage of the lamp and the time of exposure ofthe workpiece to the radiated heat. The distance of the surface from thelamp is of lesser significance because the radiation beam is containedand, at the short distance involved, virtually all of the energy fallson the workpiece. Thus the PLA controls the heat input primarily bydetermining the time of exposure rather than by regulating the distanceof the luminaire from the workpiece. Preferably the PLA controls theeffective heating time by powering down the lamps to say ten percent oftheir nominal output at the end of the required period, rather than byimmediately switching the lamps on and off. This markedly increases theworking life of the individual bulbs. The array of heating units can beraised up from its operating position close to the moulds in the heatingstation, by the thrustor 49, but this is done to facilitate thereplacement of burnt-out bulbs rather than as a heating control measure.

[0047] The heating is continued as needed to soften a surface layer ofthe workpiece. The temperature rise is confined to the surface layerbecause of the short duration of the heating and the fact thatthermoplastics foams are normally very good thermal insulators with lowcoefficients of conduction. Thus the heating has little effect on thephysical properties of the workpiece as a whole. Nevertheless it softensthe surface layer and relieves the compressive stress in the surfacelayer due to its distortion into a domed shape. In experiments leadingto the present invention it was found that provided the softened surfacelayer is maintained in the curved position until it has cooled andre-hardened, then its resistance to tensile strain is sufficient torender the domed shape of the workpiece as a whole self sustaining.

[0048] At the end of the heating step, which is always of more durationthan the almost instantaneous insertion step, the PLA causes theconveyor means to operate and shifts the batch of the moulds from theheating station 34 into the cooling station 35.

[0049] The cooling station 35 may be no more than a length of theconveyor path that is exposed to room temperature. Cooling is normallyslower than heating and in the present instance the length of conveyorin the cooling station is such that each batch of moulds normally dwellsin the cooling station for two of the dwell times applicable to the,insertion, heating and unloading stations. Of course that could beextended to further dwells in the cooling station, or forced coolingcould be employed, if only a short dwell time is needed in the heatingstation, for example, due to increasing the wattage of the heatingunits.

[0050] On the next operation of the conveyor means, the batch of mouldsthen progresses into the unloading station 36. Having passed around thedriving pulley 24, the batch of moulds arrives in the unloading stationin an inverted disposition.

[0051] The ejection means of the unloading station are virtually thesame as the insertion means. They comprise a platen frame 55 able torise and fall under the influence of two double acting pneumaticthrustors 56 (one near each end of the frame 41) on two pairs of guiderods 57, and fifty-seven plungers 58 in respective alignment with themoulds in the unloading station.

[0052] As may best be seen in FIGS. 14 and 15, each plunger 58 comprisesa plunger rod 59 and a plunger head 60, which distinguishes it from theplunger head 45 of the insertion means. The plunger head 60 comprises aplate 61, two struts 62 and a thick-walled tubular element 63 with aconcave annular end face 64 conforming to the convex surface of theshaped workpiece 37. As the plunger 58 descends from the upper (FIG. 14)position to the lower (FIG. 15) position it pushes the workpiece 37ahead of it from the mould cavity to fall into a box or other collectioncontainer (not shown).

[0053] Whilst not shown in the drawings, the apparatus of the presentinvention is provided with an array of light emitting diodes (LEDs) eachof which is adjacent and associated with a respective heating unit 50.The LEDs are wired to the heating circuit in such a manner, that when abulb of a heating unit 50 bums out, the LED associated with the burntout LED lights up indicating that location of the burnt out bulb

[0054] In other embodiments of the invention functionally similaroperating means may be used in the respective operating stations. Forexample means other than pneumatic thrusters may be used to shift theplaten frames or their equivalent in the insertion and unloadingstation. The incandescent light bulbs of the heating station may bereplaced by other heating devices. For example the concave surface ofthe workpiece may be heated by a brief exposure to a flame or other hotgas, by exposure to a radiant heating element, or by contact with apart-spherical hot “plate” or otherwise, sufficiently to cause a thinsurface layer to melt without affecting the bulk of the precursormaterial below that surface.

1. A method of making a dome-shaped article from a workpiece ofthermoplastics sheet material, comprising the steps of selecting aworkpiece of thermoplastics foam sheet material in the form of asubstantially flat, flexible disk having a smoothly curved periphery,forcing the workpiece into a mould cavity having a cross-section with aperiphery of substantially the same shape as that of the workpiece butof smaller size, so as to cause the workpiece to adopt a domed shapedisplaying a concave side, heating said concave side to soften a surfacelayer thereof, then ceasing said heating to allow said surface layer tocool and harden to cause the workpiece to become self-sustaining inshape, and then removing the shaped workpiece from the mould cavity. 2.A method according to claim 1 wherein the step of forcing the workpieceinto the mould cavity is effected by relative movement of a convex headand said mould.
 3. A method according to claim 2 wherein said convexhead conforms to the shape of the concave side of the workpiece.
 4. Amethod according to claim 1 wherein said step of heating is effected bydirecting radiant energy onto said concave side of the workpiece.
 5. Amethod according to claim 1 wherein said step of heating is effected bydirecting a hot fluid onto said concave side of the workpiece.
 6. Amethod according to claim 1 wherein said step of heating is effected bycontacting said concave side of the workpiece with a complementaryconvex hot body.
 7. A method according to claim 1 wherein said cavity isopen ended and said step of removing is effected by pushing the cooledworkpiece through one end of the cavity.
 8. A method according to claim1 wherein said article is a sealing element for a vaginal speculum andsaid workpiece is an annulus.
 9. A method according to claim 8 whereinsaid plastics foam is a closed cell polyethylene foam.
 10. Apparatus foreffecting the method of claim 1 comprising a mould defining said cavity,a loading station wherein said workpiece may be applied to the mould torest on the mould to cover a mouth of said cavity, an insertion stationwherein insertion means force the workpiece into said cavity so as tocause the workpiece to adopt a domed shape with a concave side directedtowards the mouth of the cavity, a heating station wherein heating meansheat the concave side of the workpiece in the mould cavity, a coolingstation wherein the heated concave side of the workpiece is allowed tocool in the mould cavity, and an unloading station wherein ejectionmeans remove the shaped workpiece from the cavity, conveyor means toshift the mould from station to station, and control means to effectcoordinated operation of the conveyor means and the insertion means,heating means and ejection means.